Precise control of electrically-controlled proportional flow valves presents a significant challenge, especially when the flow valve is expected to precisely follow an arbitrary trajectory over time, or when the trajectory has rapid acceleration over different ranges of flow. Typical valve characteristics are such that sensitivity of flow to command is very low at the low flow range and much higher at the higher flow range. Because this difference in sensitivity can often be several orders of magnitude, precise control of a proportional flow valves over the full range of possible flow rates is problematic.
In an attempt to provide precision and accuracy, proportional flow valve designers have applied feedback into valve positioning controls that measure and analyze the outlet flow of the valve. With such large differences in valve sensitivity ordinary closed loop controls tend to respond differently depending on what range of flow they are commanded to operate. Accordingly, proportional flow valve designers often modify the control loop gain according to the current operating flow range, and knowledge of the valve sensitivity. However, this can result in additional problems including, for example, that: (1) a requirement that the valve be calibrated prior to operation to determine its sensitivity profile might be introduced; (2) valve sensitivity profiles may be significantly different over a population of valves; (3) the valve upstream pressure changes or varies, thus changing valve sensitivity; and (4) the valve sensitivity may change after a calibration has been done by such effects as temperature changes, wear of valve mechanical components, or any other disturbing influences that tend to change the valve position to flow profile. Operating the closed loop flow control gain adjustments under an assumed flow sensitivity can lead to poor response behavior, or worse instability if the profile changes, and so this approach can present risk where the flow control is critical such as in life support.
Accordingly, there is a need in the art for a specialized flow valve control method that automatically determines required instantaneous gain adjustments without the need for prior valve profile information. Further, there is a need in the art for simple, direct, and efficient flow valve controls systems and methods that do not require a calibration of the valve.